The goal of this project is to develop an implantable micro-transponder for measurement of interstitial fluid pressure (IFP) in solid tumors. IFP is an important clinical parameter indicating the accessibility of many solid tumors to therapeutic agents. This is in light of the fact that higher levels of IFP in tumors impede the efficient delivery of drugs. In addition to chemotherapy, radiation therapy can also benefit from lowering the IFP by increasing the oxygen partial pressure in hypoxic tumor regions. The ability to measure IFP using an implantable micro-transponder would provide valuable data for evaluating various pharmacological agents used to lower the IFP. In addition, by measuring the IFP, one can tailor the administration of IFP lowering drugs to optimize their efficacy (e.g., administration of the chemotherapeutic agent when the IFP is reduced). During the course of the proposed research we will develop a micro-transponder for wireless measurement of IFP inside solid tumors. The micro-device consists of a capacitive pressure sensor with an integrated Guyton capsule connected to an inductor, thus forming a parallel LC circuit whose resonant frequency is a measure of interstitial pressure. The LC resonator is packaged inside a glass tube (1.5mm in diameter and 1cm in length) with the Guyton capsule side exposed to the tissue. The presence of Guyton capsule allows accurate measurements of IFP following the implantation since interstitial fluid can easily ingress into the device.